BACKGROUND: In 2021, four patients who had received solid organ transplants in the USA developed encephalitis beginning 2-6 weeks after transplantation from a common organ donor. We describe an investigation into the cause of encephalitis in these patients. METHODS: From Nov 7, 2021, to Feb 24, 2022, we conducted a public health investigation involving 15 agencies and medical centres in the USA. We tested various specimens (blood, cerebrospinal fluid, intraocular fluid, serum, and tissues) from the organ donor and recipients by serology, RT-PCR, immunohistochemistry, metagenomic next-generation sequencing, and host gene expression, and conducted a traceback of blood transfusions received by the organ donor. FINDINGS: We identified one read from yellow fever virus in cerebrospinal fluid from the recipient of a kidney using metagenomic next-generation sequencing. Recent infection with yellow fever virus was confirmed in all four organ recipients by identification of yellow fever virus RNA consistent with the 17D vaccine strain in brain tissue from one recipient and seroconversion after transplantation in three recipients. Two patients recovered and two patients had no neurological recovery and died. 3 days before organ procurement, the organ donor received a blood transfusion from a donor who had received a yellow fever vaccine 6 days before blood donation. INTERPRETATION: This investigation substantiates the use of metagenomic next-generation sequencing for the broad-based detection of rare or unexpected pathogens. Health-care workers providing vaccinations should inform patients of the need to defer blood donation for at least 2 weeks after receiving a yellow fever vaccine. Despite mitigation strategies and safety interventions, a low risk of transfusion-transmitted infections remains. FUNDING: US Centers for Disease Control and Prevention (CDC), the Biomedical Advanced Research and Development Authority, and the CDC Epidemiology and Laboratory Capacity Cooperative Agreement for Infectious Diseases.

Heartland virus (HRTV) disease is an emerging tickborne illness in the midwestern and southern United States. We describe a reported fatal case of HRTV infection in the Maryland and Virginia region, states not widely recognized to have human HRTV disease cases. The range of HRTV could be expanding in the United States.

With increasing use of rituximab and other B-cell depleting monoclonal antibodies for multiple indications, infectious complications are being recognized. We summarize clinical findings of patients on rituximab with arboviral diseases identified through literature review or consultation with the Centers for Disease Control and Prevention. We identified 21 patients on recent rituximab therapy who were diagnosed with an arboviral disease caused by West Nile, tick-borne encephalitis, eastern equine encephalitis, Cache Valley, Jamestown Canyon, and Powassan viruses. All reported patients had neuroinvasive disease. The diagnosis of arboviral infection required molecular testing in 20 (95%) patients. Median illness duration was 36 days (range, 12 days-1 year) and 15/19 (79%) patients died from their illness. Patients on rituximab with arboviral disease can have a severe or prolonged course with an absence of serologic response. Patients should be counseled about mosquito and tick bite prevention when receiving rituximab and other B-cell depleting therapies.

BACKGROUND: Tick-borne encephalitis (TBE) is an arboviral disease that is focally endemic in parts of Europe and Asia. TBE cases among US travellers are rare, with previous reports of only six cases among civilian travellers through 2009 and nine military-related cases through 2020. A TBE vaccine was licenced in the USA in August 2021. Understanding TBE epidemiology and risks among US travellers can help with the counselling of travellers going to TBE-endemic areas. METHODS: Diagnostic testing for TBE in the USA is typically performed at the Centers for Disease Control and Prevention (CDC) because no commercial testing is available. Diagnostic testing for TBE at CDC since 2010 was reviewed. For individuals with evidence of TBE virus infection, information was gathered on demographics, clinical presentations and risk factors for infection. RESULTS: From 2010-20, six patients with TBE were identified. Cases occurred among both paediatric and adult travellers and all were male. Patients were diagnosed with meningitis (n = 2) or encephalitis (n = 4); none died. Cases had travelled to various countries in Europe or Russia. Three cases reported visiting friends or relatives. Activities reported included hiking, camping, trail running, or working outdoors, and two cases had a recognized tick bite. CONCLUSIONS: TBE cases among US travellers are uncommon, with these six cases being the only known TBE cases among civilian travellers during this 11-year period. Nonetheless, given potential disease severity, pre-travel counselling for travellers to TBE-endemic areas should include information on measures to reduce the risk for TBE and other tick-borne diseases, including possible TBE vaccine use if a traveller's itinerary puts them at higher risk for infection. Clinicians should consider the diagnosis of TBE in a patient with a neurologic or febrile illness recently returned from a TBE-endemic country, particularly if a tick bite or possible tick exposure is reported.

BACKGROUND: The United States military regularly deploys thousands of service members throughout areas of South America and Africa that are endemic for yellow fever (YF) virus. To determine if booster doses might be needed for service members who are repetitively or continually deployed to YF endemic areas, we evaluated seropositivity among US military personnel receiving a single dose of YF vaccine based on time post-vaccination. METHODS: Serum antibodies were measured using a plaque reduction neutralization test with 50% cutoff in 682 military personnel at 5-39 years post-vaccination. We determined noninferiority of immune response by comparing the proportion seropositive among those vaccinated 10-14 years previously with those vaccinated 5-9 years previously. Noninferiority was supported if the lower-bound of the 2-tailed 95% CI for p(10-14years) - p(5-9years) was ≥-0.10. Additionally, the geometric mean antibody titer (GMT) at various timepoints following vaccination were compared to the GMT at 5-9 years. RESULTS: The proportion of military service members with detectable neutralizing antibodies 10-14 years after a single dose of YF vaccine (95.8%, 95% CI 91.2-98.1%) was non-inferior to the proportion 5-9 years after vaccination (97.8%, 95% CI 93.7-99.3%). Additionally, GMT among vaccine recipients at 10-14 years post vaccination (99, 95% CI 82-121) was non-inferior to GMT in YF vaccine recipients at 5-9 years post vaccination (115, 95% CI 96-139). The proportion of vaccinees with neutralizing antibodies remained high, and non-inferior, among those vaccinated 15-19 years prior (98.5%, 95%CI 95.5-99.7%). Although the proportion seropositive decreased among vaccinees ≥ 20 years post vaccination, >90% remained seropositive. CONCLUSIONS: Neutralizing antibodies were present in > 95% of vaccine recipients for at least 19 years after vaccination, suggesting that booster doses every 10 years are not essential for most U.S. military personnel.

BACKGROUND: In fall 2017, 3 solid organ transplant (SOT) recipients from a common donor developed encephalitis within 1 week of transplantation, prompting suspicion of transplant-transmitted infection. Eastern equine encephalitis virus (EEEV) infection was identified during testing of endomyocardial tissue from the heart recipient. METHODS: We reviewed medical records of the organ donor and transplant recipients and tested serum, whole blood, cerebrospinal fluid, and tissue from the donor and recipients for evidence of EEEV infection by multiple assays. We investigated blood transfusion as a possible source of organ donor infection by testing remaining components and serum specimens from blood donors. We reviewed data from the pretransplant organ donor evaluation and local EEEV surveillance. RESULTS: We found laboratory evidence of recent EEEV infection in all organ recipients and the common donor. Serum collected from the organ donor upon hospital admission tested negative, but subsequent samples obtained prior to organ recovery were positive for EEEV RNA. There was no evidence of EEEV infection among donors of the 8 blood products transfused into the organ donor or in products derived from these donations. Veterinary and mosquito surveillance showed recent EEEV activity in counties nearby the organ donor's county of residence. Neuroinvasive EEEV infection directly contributed to the death of 1 organ recipient and likely contributed to death in another. CONCLUSIONS: Our investigation demonstrated EEEV transmission through SOT. Mosquito-borne transmission of EEEV to the organ donor was the likely source of infection. Clinicians should be aware of EEEV as a cause of transplant-associated encephalitis.

In 2016, Zika virus disease developed in a man (patient A) who had no known risk factors beyond caring for a relative who died of this disease (index patient). We investigated the source of infection for patient A by surveying other family contacts, healthcare personnel, and community members, and testing samples for Zika virus. We identified 19 family contacts who had similar exposures to the index patient; 86 healthcare personnel had contact with the index patient, including 57 (66%) who had contact with body fluids. Of 218 community members interviewed, 28 (13%) reported signs/symptoms and 132 (61%) provided a sample. Except for patient A, no other persons tested had laboratory evidence of recent Zika virus infection. Of 5,875 mosquitoes collected, none were known vectors of Zika virus and all were negative for Zika virus. The mechanism of transmission to patient A remains unknown but was likely person-to-person contact with the index patient.

BACKGROUND: In 2014, we investigated a cluster of Guillain-Barre syndrome (GBS) in Fiji that occurred during a dengue epidemic. We designed a case-control study to determine the etiology. METHODS: Cases were patients meeting Brighton Collaboration criteria for GBS with onset from February 2014 to May 2014. Controls were persons without symptoms of GBS who were matched by age group and location. We collected information on demographics and potential exposures. Serum samples were tested for evidence of recent arboviral or Leptospira spp. infections. RESULTS: Nine cases of GBS were identified for an incidence of five cases per 100,000 population/year. Median age of cases was 27years (range: 0.8-52); five (56%) were male. Six (67%) reported an acute illness prior to GBS onset. Among the 9 cases and 28 controls enrolled, odds ratios for reported exposures or antibodies against various arboviruses or Leptospira spp. were not statistically significant. CONCLUSIONS: No clear etiologies were identified for this unusual GBS cluster. There was a temporal association between the GBS cluster and a dengue epidemic, but we were unable to substantiate an epidemiologic or laboratory association. Further study is needed to explore potential associations between arboviral infections and GBS.

Eastern Equine Encephalitis virus (EEEV) is a medically important pathogen that can cause severe encephalitis in humans, with mortality rates ranging from 30 to 80%. Unfortunately there are no antivirals or licensed vaccines available for human use, and laboratory diagnosis is essential to differentiate EEEV infection from other pathogens with similar clinical manifestations. The Arboviral Diseases Branch (ADB) reference laboratory at the CDC Division of Vector-Borne Diseases (DVBD) produces reference antigens used in serological assays such as the EEEV immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA). However, EEEV is classified as a HHS select agent and requires biosafety level (BSL) three containment, limiting EEEV antigen production in non-select agent and BSL-2 laboratories. A recombinant Sindbis virus (SINV)/EEEV has been constructed for use under BSL-2 conditions and is not regulated as a select agent. Cell culture production of inactivated EEEV antigen from SINV/EEEV for use in the EEEV MAC-ELISA is reported here. Cell culture conditions and inactivation procedures were analyzed for SINV/EEEV using a recently developed antigen production algorithm, with the MAC-ELISA as the performance indicator.

Arboviruses are medically important pathogens that cause human disease ranging from a mild fever to encephalitis. Laboratory diagnosis is essential to differentiate arbovirus infections from other pathogens with similar clinical manifestations. The Arboviral Diseases Branch (ADB) reference laboratory at the CDC Division of Vector-Borne Diseases (DVBD) produces reference antigens used in serological assays such as the virus-specific immunoglobulin M antibody-capture enzyme-linked immunosorbent assay (MAC-ELISA). Antigen production in cell culture has largely replaced the use of suckling mice; however, the methods are not directly transferable. The development of a cell culture antigen production algorithm for nine arboviruses from the three main arbovirus families, Flaviviridae, Togaviridae, and Bunyaviridae, is described here. Virus cell culture growth and harvest conditions were optimized, inactivation methods were evaluated, and concentration procedures were compared for each virus. Antigen performance was evaluated by the MAC-ELISA at each step of the procedure. The antigen production algorithm is a framework for standardization of methodology and quality control; however, a single antigen production protocol was not applicable to all arboviruses and needed to be optimized for each virus.

U.S. National Park Service employees may have prolonged exposure to wildlife and arthropods, placing them at increased risk of infection with endemic zoonoses. To evaluate possible zoonotic risks present at both Great Smoky Mountains (GRSM) and Rocky Mountain (ROMO) National Parks, we assessed park employees for baseline seroprevalence to specific zoonotic pathogens, followed by evaluation of incident infections over a 1-year study period. Park personnel showed evidence of prior infection with a variety of zoonotic agents, including California serogroup bunyaviruses (31.9%), Bartonella henselae (26.7%), spotted fever group rickettsiae (22.2%), Toxoplasma gondii (11.1%), Anaplasma phagocytophilum (8.1%), Brucella spp. (8.9%), flaviviruses (2.2%), and Bacillus anthracis (1.5%). Over a 1-year study period, we detected incident infections with leptospirosis (5.7%), B. henselae (5.7%), spotted fever group rickettsiae (1.5%), T. gondii (1.5%), B. anthracis (1.5%), and La Crosse virus (1.5%) in staff members at GRSM, and with spotted fever group rickettsiae (8.5%) and B. henselae (4.3%) in staff at ROMO. The risk of any incident infection was greater for employees who worked as resource managers (OR 7.4; 95% CI 1.4,37.5; p=0.02), and as law enforcement rangers/rescue crew (OR 6.5; 95% CI 1.1,36.5; p=0.03), relative to those who worked primarily in administration or management. The results of this study increase our understanding of the pathogens circulating within both parks, and can be used to inform the development of effective guidelines and interventions to increase visitor and staff awareness and help prevent exposure to zoonotic agents.

BACKGROUND: Chikungunya virus (CHIKV) represents a threat to the United States, because humans amplify CHIKV and vectors that transmit CHIKV are present. METHODS: We described the epidemiology of laboratory-confirmed chikungunya fever (CHIK) cases in the United States in 1995-2009 and compared states with CHIKV vectors with states with returning viremic CHIK cases. For 2006-2009, we evaluated reporting of CHIK cases to ArboNET, the arboviral surveillance system. RESULTS: In 1995-2009, 109 CHIK cases were identified in the United States; all adult travelers. Sixty-two subjects (57%) had recently visited India, and 13 (12%) had CHIKV viremia. Of the 26 jurisdictions with CHIK cases, 22 (85%) reported the presence of CHIKV vectors. Twelve viremic travelers returned to 6 states with CHIKV vectors. Of the 106 cases identified in 2006-2009, only 27 (25%) were reported to ArboNET, with a median of 122 days (range, 44-273 days) between illness onset and reporting. CONCLUSIONS: No locally acquired CHIK cases were identified. However, several viremic travelers returned to states with CHIKV vectors and presented a risk for local transmission. Incomplete and delayed reporting made ArboNET less useful. To minimize the risk of CHIKV spread in the United States, healthcare providers and public health officials should be educated about recognition, diagnosis, and reporting of CHIK cases.

From September through early December 2005, an outbreak of yellow fever (YF) occurred in South Kordofan, Sudan, resulting in a mass YF vaccination campaign. In late December 2005, we conducted a serosurvey to assess YF vaccine coverage and to better define the epidemiology of the outbreak in an index village. Of 552 persons enrolled, 95% reported recent YF vaccination, and 25% reported febrile illness during the outbreak period: 13% reported YF-like illness, 4% reported severe YF-like illness, and 12% reported chikungunya-like illness. Of 87 persons who provided blood samples, all had positive YF serologic results, including three who had never been vaccinated. There was also serologic evidence of recent or prior chikungunya virus, dengue virus, West Nile virus, and Sindbis virus infections. These results indicate that YF virus and chikungunya virus contributed to the outbreak. The high prevalence of YF antibody among vaccinees indicates that vaccination was effectively implemented in this remotely located population.